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Abstract

Many randomized controlled trials (RCTs) have been done on role of probiotics as a
treatment modality in allergic rhinitis. We conducted a review on the same. A systematic
search of published literature was done. RCTs comparing effect of probiotics with
placebo were included. A predefined set of outcome measures were assessed. Continuous
data were expressed as pooled standardized mean difference (SMD) with 95% confidence
interval (CI). Dichotomous data were expressed as odds ratio with 95% CI. P value < 0.05 was considered significant. RevMan version 5 was used for all the analyses.
Seven RCTs were eligible for inclusion. Probiotic intake improved quality of life
score in patients with allergic rhinitis [SMD -1.17 (95% CI -1.47, -0.86; P < 0.00001)]. Other parameter that improved with probiotic intake was decrease in the
number of episodes of rhinitis per year. There was no significant change in blood
or immunologic parameters in the probiotic group, SMD -0.10 (95% CI -0.26, 0.06; P = 0.22). Adverse events were not significant. Probiotic therapy might be useful in
rhinitis, but the present data do not allow any treatment recommendations.

Keywords:

Introduction

In the past 4 decades, there has been a marked increase in the prevalence of allergic
rhinitis (AR) in urban settings and a smaller rise in rural areas. In prosperous societies,
20-40% of children suffer from AR [1]. There is currently no cure for, though a wide range of treatments are employed to
control the symptoms. Many of the treatment modalities do not act through modification
of inflammatory pathways which underlies the pathophygiologic basis of these diseases.

Probiotics are live micro-organisms that confer a beneficial physiological effect
on the host when administered in adequate amounts [2]. Limited evidence from systematic reviews shows that probiotics are beneficial for
treating infectious diarrhea, preventing antibiotic-associated diarrhea, and treating
vaginal infections in pregnancy [3-5]. They have been formally investigated in a number of clinical trials for the treatment
of seasonal and perennial AR with variable results. The aim of the present paper is
to find whether probiotics are effective in treatment of AR or not.

Method

Criteria for Considering Studies for This Review

Types of Studies

Randomized double-blind placebo-controlled trials (RCTs).

Types of Participants

Participants in trials were of either sex and of any age.

Types of Interventions

Interventions consisted of daily treatment with probiotics or placebo (no probiotic
bacteria), used for > 2 weeks, as an additive to standard antiallergic medications.
All formulations of probiotics (irrespective of the type, strain, and concentration)
were considered.

Types of Outcome Measures

A. Primary outcome

Quality of life score at the end of treatment

B. Secondary outcomes

Time (months) free from episodes.

Mean duration of an episode.

Number of episodes per year.

Changes in blood parameters/immunologic markers.

Time or duration was defined was defined as number of days to resolution of specific
outcome from initiation of treatment. Change in symptom score was defined as the change
in total score over days per week. If the data were not available in the required
format, the authors were contacted for the information.

Search Methods for Identification of Studies

We systematically searched Medline, Cochrane Central Register of Controlled Trials
(CENTRAL), EMBASE and previous reviews including cross references (all articles referenced),
abstracts, and conference proceedings for all relevant articles till June 2010. Following
keywords: "probiotics" OR "lactobacillus" OR "bifidobacterium" OR "bacterio-therapy"
OR "fermented milk" OR "lactic acid bacteria" AND "supplement" OR "treatment" AND
"allergy" OR "respiratory allergy" OR "allergic rhinitis" AND "children" OR "pediatric"
OR "adults" AND "clinical trial" OR "randomized controlled trial" were used for retrieval
of relevant articles. No language restrictions were applied. Two investigators carried
out the search independently. We then combined all the searches and retrieved the
relevant articles. Manual search was made by going through the reference lists of
the retrieved articles and through Index Medicus and key allergy, asthma, and immunology
journals.

Data Collection and Analysis

Methodological Quality

Each included study was evaluated with the (previously validated) 5-point Jadad scale
to assess quality of trials by 2 independent reviewers [6]. This scale assigns points as follows:

1. Was the study described as randomized? (0 = no; 1 = yes)

2. Was the study described as double-blind? (0 = no; 1 = yes)

3. Was there a description of withdrawals and drop-outs? (0 = no; 1 = yes)

4. Was the method of randomization well described and appropriate? (0 = no; 1 = yes)

5. Was the method of double blinding well described and appropriate? (0 = no; 1 =
yes)

6. Deduct 1 point if methods for randomization or blinding were inappropriate.

Out of maximum possible score of 5, studies with scores ≥ 3 are supposed to be of
good qualities were included in the analysis.

Data Collection

Two review authors independently reviewed the results for inclusion in the analysis.
Design of the trial, comparator, characteristics of study participants, number of
participants, type of intervention (dose, duration), and major outcomes evaluated.
Differences about study quality were resolved through discussion. We recorded data
on a prestructured data extraction form. We assessed publication bias using the Cochrane
Collaboration's 'Risk of bias' tool.

Study Descriptions

Information in relation to methodological quality, characteristics of participants,
interventions and outcome measures of each trial is provided in Table 1.

Data Synthesis

Continuous data were expressed as mean (SD) and standardized mean difference (SMD)
was obtained. The data from various studies were pooled and expressed as pooled SMD
with 95% confidence interval (CI). Dichotomous data were expressed as odds ratio (OR)
with 95% CI. P value < 0.05 was considered significant. A fixed effects model was initially conducted.
If significant heterogeneity existed between trials, potential sources of heterogeneity
were considered and where appropriate a random effects model was used. Inverted funnel
plot was generated for assessment of publication bias. RevMan (Version 5) was used
for all the analyses.

Results

There were 53 hits obtained when the combined MeSH terms were used (Figure 1). From the initial search, 11 studies were considered as potentially eligible. These
studies were further evaluated for eligibility. Seven studies were found to be eligible
for inclusion in this review (Table 1),[7-13]and 4 studies were excluded [20-23]. The quality of studies were good with Jadad score varying from 3 to 5. Though most
studies had adequate randomization and blinded intervention, allocation concealment
was not clear in all but one study [9]. Not all studies assessed all the out comes. For the studies in which the results
were expressed as mean (95% CI) or mean ± SE, the SD was derived from the available
data. Seven included studies enrolled a total of 616 participants (342 for treatment
and 274 as control subjects, which totaled 610 after losses to follow-up) involving
all age groups and both sexes. In 3 trials, participants were administered probiotics
on/before the onset of pollen season and was continued until the completion of the
pollen season [10-12]. Two studies provided data on the assessment of quality of life[7,8]and 3 about adverse-events [7,8,10].

Secondary Outcome Measures

The results could not be pooled (except for blood/immunologic parameters) as there
were single study reports.

Time (Months) Free From the Episodes

Probiotic intake has no effect on the time free from episodes of rhinitis. The mean
(95% CI) time free from episodes being 4.1 (3.1 to 5.0) months in the intervention
group versus 3.3 (2.4 to 4.3) months in the control group (P value = 0.9).

Mean Duration of an Episode

There was no significant difference between intervention and control group, [mean
1.02 (95% CI -0.27 to 2.32)].

Number of Episodes Per Year

The episodes of rhinitis were significantly lower in the intervention group with an
adjusted odds ratio (95% CI) of 0.39 (0.19 to 0.82, P < 0.01).

Changes in Blood or Immunologic Parameters

Data from 5 studies including 372 patients were used for this analysis [9-13]. Overall there was no significant change in blood or immunologic parameters in the
probiotic group, SMD -0.10 (95% CI -0.26, 0.06; P = 0.22).

Side-Effects Noted (If Any)

None of the 7 studies reported a definition of what constituted an adverse event.
Two of the 3 studies, that did monitor for adverse events reported absence of adverse
events [7,8]. The third, reported 14 minor adverse events (including cold, diarrhea, vomiting)
but not the group (treatment or control) in which they occurred [10].

Publication Bias

To assess whether there was a bias in the published literature, funnel plot was constructed
using the SMD and 1/SE (standard error of mean) of SMD values obtained from studies
for one of the secondary outcome measures (serum total IgE level) as there were paucity
of data for primary outcome measures. In the absence of a publication bias, such a
plot is expected to have a shape resembling an inverted funnel [14]. From the funnel plot generated, the possibility of publication bias in the analysis
could not be ruled out (Figure 3).

Figure 3.Funnel plot. Assessing publication bias using the SMD and 1/SE of SMD values from serum total
IgE level.

Discussion

In the present review, treatment with probiotic was shown to improve the quality of
life score of patients with AR at the end of treatment. Other outcome showing improvement
with probiotic treatment was decrease in the number of episodes of rhinitis per year.
Pooling could not be undertaken for many of the outcomes, as studies did not follow
a standard format for reporting of clinical trials. Many reasons could account for
the different outcomes among studies wherever pooling was done in these trials and
these are: varied dose and intake period, the type and severity of the symptoms involved
were different, seasonal variation of allergic symptoms and most importantly, the
species and strains of the probiotics differ.

As atopic disease have seasonal variation of symptoms, the results could have been
affected by time period of a particular study. Three studies reported effects of probiotics
on allergic symptoms induced during pollen season of Japanese cedar pollen (JCP) in
patients with history of such allergy (confirmed by symptoms and laboratory tests)
[10-12]. In these trials, participants were administered probiotics on/before the onset of
pollen season and were continued until the completion of the pollen season. BB536-supplemented
yogurt has been demonstrated to have a pronounced promoting effect on intestinal environments
after 2 weeks of intake at a dose of 100 g per day [15]. For this reason, in these studies probiotics was administrated before pollen exposure.
Another important reason is the difference regarding the validity of the clinical
effects of lactic acid bacteria among species and strains. In fact, in vitro studies
using human mononuclear cells have indicated that there are strain-dependent differences
in the ability of lactic acid bacteria to induce immunoregulatory monokines such as
interleukin 12 [16]. Contribution of the species- and strain-specific nature of lactic acid bacteria
on the efficacy of improving allergic symptoms should be considered.

Placebo was poorly defined in most of the studies. Many studies used nonfermented
milk or plain yogurt as placebo. A better control would have been fermented milk without
the addition of the probiotic bacteria or sterilized fermented milk [17]. The studies demonstrated the effect of fermented milk containing a specific probiotic
strain, but it is not possible to conclude about the effect of probiotic bacteria
per se. Indeed, studies state that plain yoghurt has some antiallergic effect and
may have impact on rhinitis and asthma [18,19]. All these trials have used different doses and durations and different strains of
probiotics (eg, bifidobacterium longum; lactobacillus strains). In all the trials,
the minimum dose of probiotics administered was > 5 billion colony forming unit (CFU)
and minimum duration of administration was 1 month. It has been hypothesized that
some probiotic strains and/or their fermentation products are responsible for improvement
of allergic rhinitis and the immunostimulatory effect of Lactobacillus may be dose
dependant [11,15,20,21].

The effects of probiotics to modulate blood/immunologic parameters associated with
allergic symptoms should be elucidated as some studies found beneficial effect on
clinical parameters without significant change in the immunologic parameters. In this
review, we found no significant overall change in immunologic parameters in the probiotics
group. In all the trials, subjects were advised to continue antiallergic medications
during symptomatic period. In contrast to other treatments such as histamine release
inhibitors or antihistamines, the effects of probiotics are expected to be mild, with
a lag period in the expression of their effect. Uses of medications vary from patient
to patient and some has carried over effects (eg, steroids). Caution should be exercised
during interpretation of results because of probiotic bacteria effects per se.

It is well known that systematic reviews are associated with limitations, and the
results obtained with these methods should be analyzed accordingly. The numbers of
patients analyzed were small to reflect the data on the whole population. Seven RCTs
included a total of 616 subjects of both age and sex with a paucity of clinically
relevant outcome measures. There was no uniformity in the definition of AR, and methodology
of conducted trials. Indeed, this meta-analysis highlights the paucity of good quality
clinical trials evaluating the role of probiotics in treatment of subjects with AR.
To conclude, though probiotic therapy might be useful in rhinitis, the present data
do not allow any treatment recommendations.